Apparatus and method for emplacing a conduit along an underground arcuate path

ABSTRACT

A method for emplacing a production casing such as a pipeline or other conduit beneath a surface obstacle such as a water course is disclosed. A drill is provided which has a trailing drill string. A pilot hole is drilled along an inverted arcuate path beneath a surface obstacle from one side to the other side of the obstacle so that the drill string occupies the pilot hole. A reamer is provided which has a relatively smaller leading end and a larger trailing end. The leading end of the reamer is attached to one of the ends of the drill string, and an end of the production casing is attached to the trailing end of the reamer. The production casing is thrust into the pilot hole at one side of the surface obstacle to project the reamer with the production casing following into the pilot hole. As the production casing is thrust into the pilot hole at one side of the obstacle, the drill string exits the pilot hole at the opposite side of the obstacle. The reamer is operated by rotating the production casing or other method simultaneously with thrusting the production casing into the pilot hole to scarify and dislodge the earth circumscribing the pilot hole. The pilot hole is enlarged to a diameter slightly greater than the production casing to provide an annulus between the production casing and the reamed hole. Drilling mud is injected through the drill string to exit at the reamer where it entrains the dislodged earth. The drilling mud containing the dislodged earth is allowed to flow into the annulus surrounding the production casing.

United States Patent 1 Cherrington 1 1 APPARATUS AND METHOD FOREMPLACING A CONDUIT ALONG AN UNDERGROUND ARCUATE PATH [76] Inventor:Martin D. Cherrington, P.O. Box

4994, Sacramento, Calif. 95825 22 Filed: July 19, 1974 [21] Appl. No.:489,979

2.349.033 5/1944 Elliott 175/53 X 2.633.334 3/1953 Lavender... 175/1712.839.271 6/1958 Kandle 175/53 3.589.135 6/1971 Ede 61/72.] 3.635.0361/1972 Hooper 6l/72.7 3.730.283 5/1973 Kostylev et a1. 175/53 3.805.8994/1974 Hicks et al 175/62 X Primary ExaminerDennis L. Taylor Alrorney,Agent, or Firm-Townsend and Townsend {57] ABSTRACT A method foremplacing a production casing such as a 1 1 July 15, 1975 pipeline orother conduit beneath a surface obstacle such as a water course isdisclosed. A drill is provided which has a trailing drill string. Apilot hole is drilled along an inverted arcuate path beneath a surfaceobstacle from one side to the other side of the obstacle so that thedrill string occupies the pilot hole. A reamer is provided which has arelatively smaller lead ing end and a larger trailing end. The leadingend of the reamer is attached to one of the ends of the drill string,and an end of the production casing is attached to the trailing end ofthe reamer. The production casing is thrust into the pilot hole at oneside of the surface obstacle to project the reamer with the produc tioncasing following into the pilot hole. As the production casing is thrustinto the pilot hole at one side of the obstacle. the drill string exitsthe pilot hole at the opposite side of the obstacle. The reamer isoperated by rotating the production casing or other methodsimultaneously with thrusting the production casing into the pilot holeto scarify and dislodge the earth circumscribing the pilot hole. Thepilot hole is enlarged to a diameter slightly greater than theproduction casing to provide an annulus between the production casingand the reamed hole. Drilling mud is injected through the drill stringto exit at the reamer where it entrains the dislodged earth. Thedrilling mud containing the dislodged earth is allowed to flow into theannulus surrounding the production casing.

15 Claims, 5 Drawing Figures APPARATUS AND METHOD FOR EMPLACING ACONDUIT ALONG AN UNDERGROUND ARCUATE PATH BACKGROUND OF THE INVENTIONThe present invention relates to a method for emplacing a productioncasing such as a pipeline or other conduit beneath a surface obstaclesuch as a water course.

The traditional method for laying pipelines, telephone cables and otherunderground conduits is to dig an open trench, lay the conduit in thetrench and then close the trench. This method is quite efficient ingeneral, but problems arise when an obstacle such as a water course or aheavily traveled road is encountered, and the conduit must traverse theobstacle.

When a road is encountered, the road must either be closed, the trafficdiverted, or parts of the road closed and the conduit laid in sections,all of which are inconvenient and interfere substantially with the useof the road. When a conduit must span a water course, other problemsarise. First, the trench must be dug to a depth considerably below thelevel at which the conduit is to be laid since the current willpartially fill the trench before the conduit can be inserted. This is asignificant problem because such trenches have a generally triangularcross section, and the volume of dirt which must be removed increaseswith the square of the depth of the trench. Such trenching also stirsthe alluvium at the bottom of the water course interfering with thenatural flora.

Even after a trench has been dug in a water course, difficulties arisein placing the conduit therein. One method of placing the conduit is tofloat it across the span of the water course and then remove itsbuoyancy to sink the pipe into the trench. The difficulty with thismethod is that the water course must be closed to traffic, floatingobjects are trapped by the floating conduit, the current of the riverbends the conduit, and when the conduit is sunk, it quite often missesthe trench. A second method is to attach a sled or skid to the leadingend of the conduit, and drag this leading end through the trench to laythe conduit. With this method, the conduit must be coated with asubstance to give it negative buoyancy, and this coating is quiteexpensive since the entire length of the conduit must be so coated.

In my previously filed patent application entitled, APPARATUS ANDPROCESS FOR DRILLING UN DERGROUND ARCUATE PATHS," Ser. No. 421,548, nowpending, a method for drilling along an inverted underground arcuatepath under a surface obstacle is disclosed. However, such methods areused primarily for drilling a relatively small pilot hole which must besignificantly enlarged in order that a production casing such as apipeline, telephone cable and other underground conduits can be placedtherein.

One of the methods which has been tried experimentally to enlarge anarcuate pilot hole so that a production casing can be placed therein hasbeen to pull a reamer through the pilot hole with the drill string usedin drilling the pilot hole, and having a larger drill string trailingthe reamer. After the hole has been reamed from end to end, a productioncasing is attached to the end of the larger drill string, and the largerdrill string is dragged through the hole with the production casingfollowing to place the casing therein. However, this method wasunsuitable for several reasons. First, pulling the reamer through thearcuate hole results in the drill string knifing through the soil andthe reamer does not follow the original reamed hole. Another reason isthat pulling the production easing into the hole without providinglubricating drilling mud scars the outside of the casing, which isparticularly critical when gas or oil lines are being installed. Theresults of this method were found to be commercially unfeasible becausethe integrity of the pipeline installed could not be guaranteed, andalso the complexity and difficulty of the method did not warrant its useover other alternative methods.

SUMMARY OF THE INVENTION The present invention relates to a method foremplacing a production casing such as a pipeline or other conduit undera surface obstacle. A drill is provided having a trailing drill string.A pilot hole is drilled along an inverted arcuate path beneath theobstacle from one side to the other so that the trailing drill stringoccupies the pilot hole. A reamer is provided having a relatively smallleading end and a relatively larger trailing end, and the leading end ofthe reamer is attached to one of the ends of the drill string. Theproduction casing is attached to the trailing end of the reamer. Theproduction casing is thrust into the pilot hole to project the reamerwith the production casing following into the hole, and the drill stringexits the pilot hole at the other side of the obstacle. The reamer isrotated either by rotating the production casing or other methodsimultaneously with the thrusting of the production casing to operatethe reamer to scarify and dislodge the earth surrounding the pilot hole.The pilot hole is enlarged to a diameter at least equal to the diameterof the production casing so that the production casing is placed alongthe arcuate path as the pilot hole is being enlarged.

in the preferred embodiment of the present invention, drilling mud isinjected into the drill string so that it exits at the reamer. Thedrilling mud thus entrains the earch scarified and dislodged by thereamer. The pilot hole is reamed to a diameter slightly larger than thatof the production casing and the drilling mud with the entrained earththerein flows into this annulus. The drilling mud lubricates theproduction casing as it is thrust ino the hole so that friction on theproduction casing is minimized and there is no damage to the outersurface of the casing. Insertion of the production casing can be furtherfacilitated by matching the buoyancy of the casing to the drilling mudand the casing will slip easily into the hole.

When the surface obstacle is relatively wide, it is preferred to removeexcess drilling mud containing the entrained earth therein from thehole. A relatively small return pipe is placed internal to theproduction casing, and is connected to the annulus around the casing.Drilling mud still fills the annulus to lubricate the production casing,but the excess drilling mud exits the hole through the return pipe sothat the hole is not enlarged more than necessary and does not blow out,as described below. The diameter of the return pipe can be selected sothat the casing has neutral buoyancy and other weights are not required.

In one of the embodiments of the present invention, the reamer isnon-rotatably attached to the production casing, and the productioncasing itself is rotated in order to operate the reamer. This has thesecondary advantage that the friction between the production casing andthe sides of the hole is reduced because the casing rotates as it entersthe hole. However, the production casing is being placed along anarcuate path and the side walls of the casing are flexed upon eachrevolution of the casing. For larger diameter production casings, thisflexing can cause fatigue failure. Hence, an alternate embodiment of thepresent method is provided wherein the production casing is rotatablyattached to the reamer, so that the casing does not rotate, and a driveshaft or other mechanism is employed to operate the reamer.

The novel features which are believed to be characteristic of theinvention, both as to organization and method of operation together withfurther objects and advantages thereof will be better understood fromthe following description considered in connection with the accompanyingdrawings in which preferred embodiments of the invention are illustratedby way of example. It is to be expressly understood, however, that thedrawings are for the purpose of illustration and description only andare not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of thecompletion of the pilot hole underneath the surface obstacle;

FIG. 2 is a perspective view similar to that of FIG. 1 illustrating thereaming of the pilot hole to selected larger diameter;

FIG. 3 is a fragmentary elevation view of the reaming apparatus of thepresent invention;

FIG. 4 is a fragmentary elevation view of the reaming apparatus of thepresent invention partially cut away; and

FIG. 5 is a fragmentary elevation view of an alternate embodiment of thepresent invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drilling of the pilot holebeneath a surface obstacle such as water course 12 is illustrated by wayof reference to FIG. 1. An inclined drill rig I4 is placed in aninclined pit 16 at one side of water course 12. A drill bit 18 having atrailing drill string 20 is directed along the desired arcuate path toexit at the other side of obstacle l2. Drill string 20 comprises aplurality of interconnected drill string segments which are joined toform the drill string. After drill bit 18 emerges at the other side ofobstacle 12, drill string 20 occupies the entire pilot hole 10.

In order to enlarge pilot hole 10, the smaller leading end of afrustro-conical reamer is attached to one end of drill string 20 asillustrated in FIG. 2. In the preferred embodiment of the presentinvention, production casing 32 is non-rotatably attached to the largertrailing end of reamer 30. The production casing is forced into pilothole 10 by thrusting the casing at its trailing end using drill rig l4,and reamer 30 is operated by rotating the casing. Production casing 30can be either a steel or cement pipe such as used for oil and waterpipelines, protective casings for telephone lines and the like.Production casing 32 consists of a plurality of segments such as 34.

In the embodiment of the present invention illustrated in FIG. 2, a tube36 is attached to the leading end of drill string 20. Tube 36 isattached to a pump 38 which forces drilling mud through the drill stringto exit at the reamer. As sections of drill string 20 emerge from thepilot hole as production casing 32 is thrust therealong, the segmentsare placed in a pile 40 and tube 36 is reattached to the leading end ofthe next segment. Hence, drilling mud is continuously injected intopilot string 20 to exit at the reamer. As the segments of drill string20 are taken off the leading end thereof, segments 34 of productioncasing 32 are added at the trailing end. The drill rig 14 used fordrilling the pilot hole also acts to thrust the production casing 32into the ground in this embodiment as illustrated by arrow 42, and inthe preferred embodiment rotates the production casing as well asoperates the reamer.

The manner in which reamer 30 is interposed between drill string 20 andproduction casing 32 is illustrated in more detail in FIG. 3. Thenarrower leading end of frustro-conical reamer 30 connects nonrotatablyto drill string 20. In the preferred embodiment, the larger trailing endof reamer 30 is nonrotatably connected to production casing 32. Reamer30 has a plurality of reamer teeth 42 which enlarge pilot hole 10 to adiameter slightly larger than that of production casing 32. Thisprovides a small annulus 44 about the outer diameter of productioncasing 32. Drilling mud which is injected through drill string 20 andexits at reamer 30 flows around the reamer and entrains the earth 46scarified and dislodged by reamer teeth 42 as illustrated by arrows 48.The drilling mud containing the dislodged earth flows into the annulus44 circumscribing the production casing 32 as illustrated by arrows 50.The used drilling mud serves to lubricate production casing 32 so thatit slips easily into the enlarged hole.

When the relatively long production casing is to be placed under theground, the buoyancy of the production casing can be a critical problem.Since the density of production casing 32 with its hollow interior issubstantially less than that of the drilling mud in annulus 44 forlarger production casings, the production casing will be forced upwardlyand will distort the path of the production casing as it is beingemplaced. For smaller production casings, the density of the casing withits hollow interior is greater than that of the drilling mud and theweight of the casing distorts the path. One of the features of thepresent invention is to weight the production casing 32 so that itsdensity including the hollow interior is substantially equal to that ofthe drilling mud. In this situation, the production casing 32 will haveneutral buoyancy with respect to the drilling mud and will slip easilyinto the hole along the axis of pilot hole 10. Such neutral buoyancy canbe achieved by placing foam inside the production casing, coating thecasing, placing weights in the casing, and the like.

A preferred embodiment of the present invention wherein excess drillingmud is removed as the production casing 32 is being emplaced isillustrated by way of reference to FIG. 4. In this embodiment, drillingmud is injected through drill string 20 as illustrated by arrow aspreviously shown. This drilling mud exits at the reamer and flows intothe annulus 44 around production casing 32. However, in order to relievethe pressure of the drilling mud in annulus 44, an internal return pipe62 is provided inside production casing 32. Return pipe 62 has aplurality of extensions 64 which communicate with holes 66 in the wallsof casing 32. In this manner, a connection is provided between returnpipe 62 and annulus 44 so that excess drilling mud in the annulus canflow out through return pipe 62 as illustrated by arrow 68.

Since volumetric flow of drilling mud into the hole is generally greaterthan that which can be accommodated by annulus 44, failure to provide areturn pipe such as 62 forces the drilling mud to flow backwardly alongthe production casing 32. In the placing of a relatively long productioncasing, the pressure on the enlarged hole adjacent the reamer will berelatively large to force the mud along the entire casing. As a result,when drilling under river bottoms and the like, the hole may blow outdue to this pressure and water from the river can flow into the hole.Also, the excess drilling mud will flow into the water course andpollute the stream and destroy the natural wildlife. The provision ofreturn pipe 62 will avoid such a blow out when long production casingsare emplaced. A further advantage of the return pipe is that thediameter of the pipe can be selected so that the drilling mud willweight production casing 32 so that it has neutral buoyancy with respectto the drilling mud. Hence, a separate weighting mechanism need not beprovided to achieve neutral buoyancy.

In the preferred embodiment, pipe 62 is used to return used drilling mudas illustrated by arrows 68. However, as an alternative embodiment, apipe such as 62 can be used to inject drilling mud so that it exits nearreamer 30 rather than inject drilling mud through drill string 20. Tothis end, pipe 62 would be extended as illustrated in phantom 69 so thatthe drilling mud would be injected at reamer 30 rather than into annulus44. After the drilling mud entrains the earth scarified and dislodged byreamer 30, the used drilling mud flows into annulus 44 as in theprevious embodiments.

An alternate embodiment to those discussed above which is primarilyadapted for use with relatively large production casings is illustratedin FIG. 5. When a production casing such as casing 70 has a diameter ofgreater than approximately inches, rotating the production casing in thearcuate path can cause excessive fatigue of the casing and it ispreferred not to rotate the casing. For such large production casings70, the casing is rotatably attached to the trailing end of a reamersuch as 72. The leading end of reamer 72 is nonrotatably attached todrill string 74, and drilling mud is injected through drill string 74 asillustrated by arrow 76, similar to the method described above. However,reamer 72 is operated by means of a drive shaft 78 which rests along thebottom of casing 70. A pulley 80 or gear arrangement is connected toreamer 72 so that rotation of drive shaft 78 operates the reamer. As analternative, a drilling motor as known in the art can be placed at theleading end of casing 70 to operate the reamer.

In the embodiment illustrated in FIG. 5, a return pipe, such as returnpipe 62 illustrated in FIG. 4, could also be provided. Also, theproduction casing 70 could be rotated slowly (relative to the rotationof the reamer 72) to make the casing slip more easily into the hole andreduce friction thereon. Fatigue of the casing is dependent upon thespeed of rotation of the casing so that at low speed rotation may beacceptable where high speed rotation such as required to operate thereamer is not acceptable.

In many applications such as the installation of telephone lines,several smaller product pipes are installed in the production casingafter it is in place. This installation is facilitated by filling theproduction casing with a fluid such as treated water or oil and sealingthe leading ends of the product pipes before inserting them in theproduction casing. As a result, the product pipes will be at leastpartially buoyant so that they will float easily into the productioncasing.

While preferred embodiments of the present invention have beenillustrated in detail, it is apparent that modifications and adaptationsof that embodiment will occur to those skilled in the art. However, itis to be expressly understood that such modifications and adaptationsare within the spirit and scope of the present invention as set forth inthe following claims.

What I claim as new is:

1. A method for emplacing a production casing beneath a surface obstaclesuch as water course, said method comprising the steps of:

providing a drill having a trailing drill string;

drilling a pilot hole along an inverted arcuate path beneath the surfaceobstacle from a first side to a second opposite side of the obstaclewith said drill so that the drill string occupies the pilot hole withthe opposite ends of said drill string being on opposite sides of theobstacle;

providing a reamer having a relatively smaller leading end and arelatively larger trailing end; attaching the relatively smaller leadingend of the reamer to one of the ends of the drill string;

attaching an end of the production casing nonrotatably to the relativelylarger trailing end of the reamer; forcing the production casing intothe pilot hole at one side of the surface obstacle to project the reamerwith said production casing following into said pilot hole, the drillstring exiting the pilot hole at the other opposite end of the obstacle;and

rotating the production casing simultaneously with said thrusting stepto operate the reamer to scarify and dislodge the earth around the pilothole to enlarge the pilot hole to a diameter at least equal to theproduction casing so that said production casing is emplaced along thearcuate path as the pilot hole is being enlarged.

2. A method as recited in claim 1 wherein said forcing comprisesthrusting the production casing at its trailing end.

3. A method as recited in claim I wherein rotating the production casingto operate the reamer is adapted to enlarge the pilot hole to a diameterslightly larger than the diameter of the production casing to provide anarrow annulus circumscribing said production casing, said methodadditionally comprising the steps of injecting drilling mud into the endof the drill string opposite from the end of the drill string attachedto the leading end of the reamer so that said drilling mud flows throughsaid drill string to exit at the reamer; entraining in said drilling mudthe earth scarified and dislodged by the reamer; and allowing thedrilling mud containing the scarified earth to flow into the annulusaround the production casing to lubricate the casing as it is forcedinto the pilot hole.

4. A method as recited in claim 1 wherein rotating the production casingto operate the reamer is adapted to enlarge the pilot hole to a diameterslightly larger than the diameter of the production casing, said methodadditionally comprising the steps of providing an inlet pipe internal tothe production casing, said inlet pipe having one end terminatingadjacent the reamer; injecting drilling mud into the inlet pipe so thatsaid drilling mud flows through said inlet pipe to exit at the reamer;entraining in said drilling mud the earth scarified by the reamer; andallowing the drilling mud containing the scarified earth to flow intothe annulus around the production casing.

5. A method as recited in claim 1 wherein attaching the leading end ofthe reamer to one of the ends of the drill string comprises attachingthe leading end of the reamer to the end of the drill string at saidfirst side of the surface obstacle.

6. A method as recited in claim 1 wherein said attaching the leading endof the reamer to one of the ends of the drill string comprises attachingthe leading end of the reamer to the end of the drill string at saidsecond side of the surface obstacle.

7. A method as recited in claim 1 wherein said trailing drill stringcomprises a plurality of drill string segments, and additionallycomprising the step of removing the segments individually from the drillstring as said drill string segments exit the pilot hole at the oppositeend of the obstacle.

8. A method as recited in claim 1 and additionally comprising the stepof providing an inclined drill rig at the first side of the surfaceobstacle, and wherein said drilling step additionally includes thrustingthe drill string into the pilot hole with said drill rig, wherein saidproduction casing forcing step additionally includes thrusting theproduction casing with said drilling rig, and wherein said productioncasing rotating step additionally includes rotating the productioncasing with said inclined drill rig.

9. A method as recited in claim 1 and additionally comprising the stepsof filling the emplaced production casing with a liquid, and inserting aplurality of product pipes in the filled production casing, the leadingends of said product pipes being sealed to provide buoyancy to saidpipes as said pipes are inserted in the production casing.

10. A method for emplacing a large diameter production casing beneath asurface obstacle such as a water course, said method comprising thesteps of:

providing a drill having a trailing drill string;

drilling a pilot hole along an inverted arcuate path beneath the surfaceobstacle from one side to the other with said drill so that the trailingdrill string occupies the pilot hole with the opposite ends of saiddrill string being on opposite sides of the obstacle;

providing a reamer having a relatively smaller leading end and arelatively larger trailing end;

attaching the leading end of the reamer to one of the ends of the drillstring;

attaching an end of the large diameter production casing to the trailingend of the reamer; providing means for rotating the reamer internal tothe production casing,

forcing the production easing into the pilot hole to project the reamerwith said production casing following into said pilot hole; and

rotating the reamer with said rotating means simultaneously with saidforcing step to operate the reamer to scarify and dislodge the eartharound the pilot hole to thereby enlarge the pilot hole to a diameter atleast equal to the production casing so that the said production casingis emplaced along the arcuate path as the pilot hole is being enlarged.

1 1. A method as recited in claim 10 wherein said providing means forrotating the reamer comprises the step of providing a drive shaftinternal to the production casing, said drive shaft having a poweroutput end attached to the reamer, and wherein said rotating the reamerstep comprises rotating the reamer by rotating the drive shaftsimultaneously with said forcing step to operate the reamer.

12. A method for emplacing a production casing beneath a surfaceobstacle such as a water course, said method comprising the steps of:providing a drill having a trailing drill string; drilling a pilot holealong an inverted arcuate path beneath the surface obstacle from a firstside to a second opposite side of the obstacle with said drill so thatthe trailing drill string occupies the pilot hole with the ends of saiddrill string being on opposite sides of the obstacle; providing a reamerhaving a relatively smallerleading end and a relatively larger trailingend; attaching the leading end of the reamer to one of the ends of thedrill string; connecting an end of the production casing to the trailingend of the reamer; providing means for rotating the reamer; thrustingthe production casing into the pilot hole to project the reamer withsaid production casing following into said pilot hole; rotating thereamer with rotating means simultaneously with said thrusting step tooperate the reamer to scarify and dislodge the earth around the pilothole; injecting drilling mud into the end of the drill string oppositefrom the end of the drill string attached to the leading end of thereamer so that said drilling mud flows through said drill string to exitat the reamer; and allowing the drilling mud containing the scarifiedearth to flow into the annulus around the production casing so that theproduction casing slips easily into the enlarged hole.

13. A method as recited in claim 12 and additionally comprising thesteps of providing a return pipe internal to the production casing;providing communication between said return pipe and the outer surfaceof the production casing; and allowing the drilling mud contained in theannulus around the production casing to flow out of the productioncasing through the return pipe.

14. A method as recited in claim 12 wherein the trailing end of thereamer is nonrotatably attached to the production casing, and whereinproviding means for rotating the reamer comprises providing means forrotating the production casing to rotate the reamer.

15. A method as recited in claim 12 wherein said providing means forrotating the reamer comprises providing a drive shaft internal to theproduction casing, said drive shaft being connected to the reamer sothat rotation of the drive shaft rotates the reamer.

1. A method for emplacing a production casing beneath a surface obstaclesuch as water course, said method comprising the steps of: providing adrill having a trailing drill string; drilling a pilot hole along aninverted arcuate path beneath the surface obstacle from a first side toa second opposite side of the obstacle with said drill so that the drillstring occupies the pilot hole with the opposite ends of said drillstring being on opposite sides of the obstacle; providing a reamerhaving a relatively smaller leading end and a relatively larger trailingend; attaching the relatively smaller leading end of the reamer to oneof the ends of the drill string; attaching an end of the productioncasing non-rotatably to the relatively larger trailing end of thereamer; forcing the production casing into the pilot hole at one side ofthe surface obstacle to project the reamer with said production casingfollowing into said pilot hole, the drill string exiting the pilot holeat the other opposite end of the obstacle; and rotating the productioncasing simultaneously with said thrusting step to operate the reamer toscarify and dislodge the earth around the pilot hole to enlarge thepilot hole to a diameter at least equal to the production casing so thatsaid production casing is emplaced along the arcuate path as the pilothole is being enlarged.
 2. A method as recited in claim 1 wherein saidforcing comprises thrusting the production casing at its trailing end.3. A method as recited in claim 1 wherein rotating the production casingto operate the reamer is adapted to enlarge the pilot hole to a diameterslightly larger than the diameter of the production casing to provide anarrow annulus circumscribing said production casing, said methodadditionally comprising the steps of injecting drilling mud into the endof the drill string opposite from the end of the drill string attachedto the leading end of the reamer so that said drilling mud flows throughsaid drill string to exit at the reamer; entraining in said drilling mudthe earth scarified and dislodged by the reamer; and allowing thedrilling mud containing the scarified earth to flow into the annulusaround the production casing to lubricate the casing as it is forcedinto the pilot hole.
 4. A method as recited in claim 1 wherein rotatingthe production casing to operate the reamer is adapted to enlarge thepilot hole to a diameter slightly larger than the diameter of theproduction casing, said method additionally comprising the steps ofproviding an inlet pipe internal to the production casing, said inletpipe having one end terminating adjacent the reamer; injecting drillingmud into the inlet pipe so that said drilling mud flows through saidinlet pipe to exit at the reamer; entraining in said drilling mud theearth scarified by the reamer; and allowing the drilling mud containingthe scarified earth to flow into the annulus around the productioncasing.
 5. A method as recited in claim 1 wherein attaching the leadingend of the reamer to one of the ends of the drill string comprisesattaching the leading end of the reamer to the end of the drill stringat said first side of the surface obstacle.
 6. A method as recited inclaim 1 wherein said attaching the leading end of the reamer to one ofthe ends of the drill string comprises attaching the leading end of thereamer to the end of the drill string at said second side of the surfaceobstacle.
 7. A method as recited in claim 1 wherein said trailing drillstring comprises a plurality of drill string segments, and additionallycomprising the step of removing the segments individually from the drillstring as said drill string segments Exit the pilot hole at the oppositeend of the obstacle.
 8. A method as recited in claim 1 and additionallycomprising the step of providing an inclined drill rig at the first sideof the surface obstacle, and wherein said drilling step additionallyincludes thrusting the drill string into the pilot hole with said drillrig, wherein said production casing forcing step additionally includesthrusting the production casing with said drilling rig, and wherein saidproduction casing rotating step additionally includes rotating theproduction casing with said inclined drill rig.
 9. A method as recitedin claim 1 and additionally comprising the steps of filling the emplacedproduction casing with a liquid, and inserting a plurality of productpipes in the filled production casing, the leading ends of said productpipes being sealed to provide buoyancy to said pipes as said pipes areinserted in the production casing.
 10. A method for emplacing a largediameter production casing beneath a surface obstacle such as a watercourse, said method comprising the steps of: providing a drill having atrailing drill string; drilling a pilot hole along an inverted arcuatepath beneath the surface obstacle from one side to the other with saiddrill so that the trailing drill string occupies the pilot hole with theopposite ends of said drill string being on opposite sides of theobstacle; providing a reamer having a relatively smaller leading end anda relatively larger trailing end; attaching the leading end of thereamer to one of the ends of the drill string; attaching an end of thelarge diameter production casing to the trailing end of the reamer;providing means for rotating the reamer internal to the productioncasing; forcing the production casing into the pilot hole to project thereamer with said production casing following into said pilot hole; androtating the reamer with said rotating means simultaneously with saidforcing step to operate the reamer to scarify and dislodge the eartharound the pilot hole to thereby enlarge the pilot hole to a diameter atleast equal to the production casing so that the said production casingis emplaced along the arcuate path as the pilot hole is being enlarged.11. A method as recited in claim 10 wherein said providing means forrotating the reamer comprises the step of providing a drive shaftinternal to the production casing, said drive shaft having a poweroutput end attached to the reamer, and wherein said rotating the reamerstep comprises rotating the reamer by rotating the drive shaftsimultaneously with said forcing step to operate the reamer.
 12. Amethod for emplacing a production casing beneath a surface obstacle suchas a water course, said method comprising the steps of: providing adrill having a trailing drill string; drilling a pilot hole along aninverted arcuate path beneath the surface obstacle from a first side toa second opposite side of the obstacle with said drill so that thetrailing drill string occupies the pilot hole with the ends of saiddrill string being on opposite sides of the obstacle; providing a reamerhaving a relatively smallerleading end and a relatively larger trailingend; attaching the leading end of the reamer to one of the ends of thedrill string; connecting an end of the production casing to the trailingend of the reamer; providing means for rotating the reamer; thrustingthe production casing into the pilot hole to project the reamer withsaid production casing following into said pilot hole; rotating thereamer with rotating means simultaneously with said thrusting step tooperate the reamer to scarify and dislodge the earth around the pilothole; injecting drilling mud into the end of the drill string oppositefrom the end of the drill string attached to the leading end of thereamer so that said drilling mud flows through said drill string to exitat the reamer; and allowing the drilling mud containing the scarifiedearth to flow into The annulus around the production casing so that theproduction casing slips easily into the enlarged hole.
 13. A method asrecited in claim 12 and additionally comprising the steps of providing areturn pipe internal to the production casing; providing communicationbetween said return pipe and the outer surface of the production casing;and allowing the drilling mud contained in the annulus around theproduction casing to flow out of the production casing through thereturn pipe.
 14. A method as recited in claim 12 wherein the trailingend of the reamer is nonrotatably attached to the production casing, andwherein providing means for rotating the reamer comprises providingmeans for rotating the production casing to rotate the reamer.
 15. Amethod as recited in claim 12 wherein said providing means for rotatingthe reamer comprises providing a drive shaft internal to the productioncasing, said drive shaft being connected to the reamer so that rotationof the drive shaft rotates the reamer.